This invention relates to superconductors. In particular, this invention relates to superconductors which are disposed on ceramic-type substrates, such as alumina. These superconductors, when disposed onto a substrate, might be electrical circuit elements themselves, such as stripline filters, or, might be simple electrical circuit paths.
In electronic packaging, electronic components are frequently mounted on planar ceramic substrates made from alumina, Al.sub.2 O.sub.3, with interconnections between the components being formed from a conductive thick film material deposited onto the substrate. These ceramic substrates are frequently used as carriers of electronic parts because of their cost, electrical properties and mechanical properties.
Interconnections between electronic devices mounted on ceramic substrates, in the prior art, have been principally made by depositing a paste onto the substrate, (the paste having conductive constituents which when suitably processed leaves a conductive path on the substrate), curing the paste and substrate and attaching the components appropriately. In many applications the conventional conductors used to connect components on ceramic substrates may have undesirable physical properties. For example, at high frequencies, skin effect losses attributable to the interconnection material increases substantially.
It has been known that certain materials' electrical resistivity goes to zero or nearly zero at a predetermined temperature known in the art as the transition temperature. Some recently discovered materials, such as Ytrium Barium Copper Oxide, or YBC, (YBa.sub.2 Cu.sub.3 O.sub.x) for example, demonstrate this so called superconductivity at relatively high temperatures, i.e., at or near 93 degrees Kelvin. Because these materials can demonstrate a near zero electrical resistance, at or below their transition temperature, it might be desirable, in certain applications, to use a superconductor material on a ceramic substrate for purposes of reducing electrical losses.
Depositing superconductors such as YBC onto an alumina substrate and maintaining the superconductors' ability to superconduct at temperatures above the temperature of liquid nitrogen has proven to be difficult. Previously, superconductors deposited onto a ceramic substrate such as alumina, which is widely used as a substrate, have been difficult to bond to the alumina, and, when thermally cycled, have sustained mechanical failures such as cracking and peeling away from the substrate to such an extent that the conductive path on the substrate is not usable. Other superconducting materials when deposited on a ceramic substrate such as alumina might have been "poisoned" by the ceramic such that the superconducting transition temperature changes or superconducting behavior disappears.
It is therefore an object of the present invention to provide a method of depositing a superconductor onto a ceramic substrate such as alumina such that the superconductor when deposited, is mechanically stable and free of mechanical defects in that it does not pull away from the ceramic substrate, crack, or sustain other mechanical failures. Another object of the present invention is to provide a superconductor which when deposited on a ceramic substrate is not poisoned by the ceramic material and continues to demonstrate superconductivity at temperatures above 77 degrees kelvin.